The present invention generally relates to wrenching and removal tools. More particularly, the present invention relates to a hand wrenching tool for removing fasteners, and particularly torque controlled or frangible collar fasteners.
For many decades, the aerospace industry has made use of frangible fasteners, sometimes referred to as “broached-pin” fastening systems, such as the Hi-Lok® fastening system. While there are many variations, all have in common a method of keeping the bolt or pin from rotating while a nut element is threaded onto it and tightened to a predetermined torque. Such frangible fasteners are used extensively in the aerospace industry due to their simplicity, consistently controlled pre-load torque and minimum size and weight.
FIGS. 1-3 illustrate a typical frangible fastening system. A pin 10 is extended through the objects 12 and 14 to be fastened to one another, as illustrated in FIGS. 1 and 2. The objects 12 and 14 can comprise sheets of metal of an aircraft skin, for example. The pin 10 includes a head 16 at one end and a threaded portion 18 at a generally opposite end.
The threaded portion 18 of the pin extends beyond the aligned objects 12 and 14. Access to the head 16 of the pin 10 is usually not possible, and for reasons of weight saving and aerodynamics, the heads 16 of the fasteners are typically flat so as to be flush with the skin of the aircraft structure or only to protrude slightly. The head 16 typically does not have any external “hex” or other shape to grip with a wrench to keep the pin 10 from rotating and turning. Instead, the threaded end 18 of the pin 10 is provided with an internal multi-faceted recess, such as an internal hex recess 20 into which a hex-Allen key wrench may be inserted to hold the pin 10 stationary while an internally threaded nut 22 is fastened thereto.
The nut 22 includes an internally threaded collar portion 24 and a wrenching ring 26. The wrenching ring 26 is configured to engage a socket, such as being of a hex shape. An intermediate portion between the collar 24 and the wrench ring 26 is designed to shear once a predetermined torque is achieved, resulting in the frangible wrenching ring portion 26 being removed from the collar portion 24 of the nut 22 when the applied torque exceeds a predetermined torsional loading, as illustrated in FIG. 2.
FIG. 3 illustrates a series of frangible fasteners which have been fastened so that the wrenching ring 26 has been removed and the collar 24 is attached to the pin 10 to secure the sheets or objects of material 12 and 14 to one another. Also shown are nuts 22 which have been threaded onto the threaded portion 18 of the pin 10 but not yet tightened sufficiently to remove the wrenching ring 26 portion thereof and ends of pins 10 ready to receive a nut 22 thereon. When the wrenching tool engages the wrenching ring 26 portion to apply rotational force to the threaded collar 24 and twist the nut 22 onto the pin 10 until the predetermined torsional loading or torque is exceeded, at which point the wrenching ring 26 will break off.
It is frequently desirable to loosen or remove the threaded collar 24 from the assembled fastener. The threaded collar commonly has a generally cylindrical base 28 which tapers into a smaller diameter cylindrical neck 30. The cylindrical portions of such collars 24 are narrow and are difficult to grasp with conventional tools, such as pliers, vice grip clamps, and the like. Additionally, the use of non-standard tools for loosening or removing the torque limited fastener is objectionable as such tools can damage the surfaces of the assembled parts, and fail to provide the required torque to loosen the fasteners.
Accordingly, there is a continuing need for a hand wrenching tool which is of a simple design, yet efficiently serves the purpose of loosening and removing fasteners that are commonly utilized in the aerospace industry. The present invention fulfills these needs and provides other related advantages.